Topographical variation in lipid content and morphological structure of the blubber in the striped dolphin

Abstract

Summary:We investigate stratification patterns and topographical variations in the blubber of the striped dolphin (Stenella coeruleoalba) to gain insights into its regionally-specific functions. We collected blubber from 10 stranded striped dolphins (5 females and 5 males) from the eastern coast of Spain in 2007-2009, at 11 body positions. Histological measurements (adipocyte number and area) and blubber lipid content were analysed for each position. Histological measurements revealed stratification of blubber into outer, middle, and inner layers. Both the adipocyte number and area were largest in the middle layer. The adipocyte number was higher in the outer than the inner layer, whereas the adipocyte area was higher in the inner than the outer layer. The ventral anterior position did not follow this pattern, likely due to its proximity to the acoustic blubber, which is known to have a different biochemical composition. The stratification in morphological blubber characteristics most likely reflects functional differences. The outer layer may provide structural support and act as a mechanical barrier with a minor role in energy storage. The middle layer may be responsible for thermoregulation, and the inner layer could be responsible for energy mobilization, which is favoured by its proximity to the body core and a higher vascularization. In addition, an increasing gradient from dorsal to ventral positions was observed in the mean number of adipocytes and lipid content, with the exception of the caudal region. Although both ventral and dorsal blubber can have insulator and buoyancy functions, the ventral blubber may mainly serve as an energy reserve.Keywords: Stenella coeruleoalba; cetacean; adipocytes; histology; stratification; lipid content. Estructura morfológica y variación topográfica del contenido lipídico en la grasa del delfín listadoResumen: En el presente estudio se investigaron los patrones de estratificación así como las variaciones topográficas en la grasa del delfín listado (Stenella coeruleoalba) con el fin de conocer mejor las posibles funciones regionales de este tejido. Se recolectaron muestras de grasa en 11 posiciones corporales diferentes de 10 delfines listados (5 hembras y 5 machos) varados en la costa este de España entre los años 2007 y 2009. Las medidas histológicas (número de adipocitos y área de los mismos) y el contenido lipídico se analizaron en cada una de las posiciones. Las medidas histológicas mostraron que la grasa se estratificaba en 3 capas: externa, media e interna. Tanto el número de adipocitos como su área eran mayores en la capa media. El número de adipocitos era superior en la capa externa que en la interna, mientras que el área de los adipocitos era mayor en la capa interna que en la externa. Sin embargo, la región ventral anterior no seguía este patrón, probablemente esto sea debido a que esta región se encuentra muy próxima a la grasa acústica, que es conocida por presentar una composición bioquímica diferente al resto de grasa corporal. La estratificación morfológi...

Assessing cetacean body condition: Is total lipid content in blubber biopsies a useful monitoring tool?

“…Various other studies have also shown that blubber thickness was a poor index of nutritive condition, as it was not correlated with changes in overall body fat reserves (Aguilar et al, 2007;Caon, Fialho, & Danilewicz, 2007;Evans et al, 2003;Gómez-Campos et al, 2015;Koopman, 2007;Read, 1990;Ruchonnet et al, 2006). It is well recognized across all species that blubber, in addition to its role as a deposit of energy, serves important functions as an insulator, it is involved in active thermoregulation, it streamlines the body, facilitates hydrodynamic locomotion, contributes to water balance, and provides buoyancy (Iverson, 2009).…”

“…The posterior dorsal area of mysticetes is a major site for lipid storage in both the blubber and the muscle (Lockyer et al, 1985), but this may not be the case for beaked whales, particularly if they are more similar to small odontocetes. In small odontocetes, the blubber in the thoracic-abdominal region is hypothesized to play an important role in insulation and energy storage, whereas the region posterior to the dorsal fin is thought to primarily act to maintain hydrodynamic and locomotory functions and is metabolically inert (Gómez-Campos, Borrell, Correas, & Aguilar, 2015;Koopman, 1998;Koopman et al, 2002;Tornero, Borrell, Forcada, Pubill, & Aguilar, 2004).…”

Influence of sample location on blubber cortisol concentration in striped dolphins (Stenella coeruleoalba): The importance of the reference denominator

“…The reason why the dorsal area also presented higher hormone levels measured as ng cortisol/g lipid is unclear. In striped dolphins, the dorsal area presents the lower adipocyte number and lipid content compared to the ventral locations (Gómez‐Campos et al, 2015), further hindering interpretation. Blubber has been recognized as a site of active steroid metabolism (Galligan et al, 2018) and evidence in other mammals suggests that the hormonal activity of the adipose tissue differs across body regions (Lindsay et al, 2003).…”

Validating the use of biopsy sampling in contamination assessment studies of small cetaceans

“…The blubber is the lipid-rich hypodermis that has different biological functions, such as the storage of energy, thermoregulation, buoyancy control and hydrodynamic streamlining (Pabst et al, 1999). Moreover, the blubber of marine mammals is a heterogeneous tissue composed of layers or strata (inner, middle and outer) that play different roles and exhibit different biochemical compositions (Evans et al, 2004;Struntz et al, 2004;Gómez-Campos et al, 2015). The inner and middle layers are mainly devoted to fat mobilisation and the lipid content greatly fluctuates depending on the reproductive and migratory cycle of individuals.…”

“…Fat deposition mainly occurs in the outer layer, which is considered metabolically more inert and has the primary function of thermal insulation. The outer layer is also little affected by changes in nutritive conditions (Aguilar and Borrell, 1991;Gómez-Campos et al, 2015). Moreover, blubber accumulates high concentrations of persistent organic pollutants (POPs), since organochlorine compounds are highly apolar compounds and dissolve in neutral lipids.…”